Animals made "blood-free" by isovolumic exchange perfusion with oxygen transporting perfluorochemical (PFC) emulsions do not hemorrhage despite reductions in their platelets and plasma proteins to less than 10% of control values. Their total plasma proteins approaches or exceeds normal levels in 24 hours while their platelets require 3-7 days to return to normal. Approximately 6 "new" intensly staining protein bands appear on disk gels of plasma samples at 24 hours after exchange prefusion. One of these as been demonstrated to be fibrinogen. The identity of the others in unknown. The aims of this project are to: A) Determine the time course from appearance through peak activity/concentration through return to normal levels for each of these proteins; B) Determine if the appearance of these proteins is unique to the rat or found in other species; C) Determine the identity and molecular characteristics of each protein; D) Determine their relationship to coagulation/hemostatic processes; E) Determine the extent of platelet involvement in the maintenance of hemostasis in these animals; F) Determine, with platelet and coagulation inhibitors, the relative importance of platelet vs coagulation function in the maintenance of hemostasis in the exchange perfused animal; and G) Determine functional differences between a mixed population of "mature" cells and a population of newly released "immature" cells. Eleven groups of 4 animals each will be exchange perfused to 3% hematocrits and sacrificed by exsanguination at 1, 6, 12, and 24 hours and at days 2 through 7 and day 14 following exchange. Samples will be analyzed for cell numbers, hemoglobin, hematocrit, total protein, albumin/globulin ratio, molecular weight and isoelectric point and by immunologic assay. One objective of this project is to define the relative importance of the platelets and coagulation proteins in the maintenance of hemostatic function in the "blood-free" and recovering animal. A second objective involves the identification and characterization of those proteins which appear to be preferentially returned to the circulation of the exchange perfused and recovering animal. A final objective involves determination if functional differences exist between a mature mixed population of cells and an immature population of cells. It thought that the results of these studies will aid in the understanding of hematologic and hemostatic regulatory, regenerative and control processes.